In the first shot that shows Lady Cranleigh and Sir Robert are applauding, Nyssa can be seen standing behind them on the front porch, but Nyssa had not even been introduced to them yet.
Tegan asks for a "Screwdriver", the cocktail made from vodka and orange. However, this cocktail wasn't present in the 1920s, and was not called a Screwdriver until the 1940s during World War II, almost 20 years after this story is set.